With increasing development of science and technology, the demands on heat-dissipating brushless fans become more stringent. For example, the air pressure, airflow capacity or the overall operating efficiency should comply with specified requirements. Conventionally, for reducing the noise of the operating motor of the brushless fan, the magnets of the rotor usually have chamfered edges. Due to the chamfered edges, the cogging torque of the motor is decreased, and the noise generated by the motor is reduced.
A rotor of a motor of a brushless fan is disclosed in for example Taiwanese Utility Model Patent Publication No. M358465, which is entitled “Rotor structure of DC brushless motor”. FIG. 1 is a schematic view illustrating a rotor of a brushless motor according to the prior art. As shown in FIG. 1, the rotor 1 includes a silicon steel sheet 10, a shaft 11, plural N-pole magnets 12 and plural S-pole magnets 13. The N-pole magnets 12 and the S-pole magnets 13 are alternately arranged around the silicon steel sheet 10 and discretely arranged at regular intervals d. After the brushless motor is turned on, the whole structure is suffered from the vibration of the brushless motor, and thus corresponding resonance is created. Due to the intervals d between the N-pole magnets 12 and the S-pole magnets 13, the cogging torque of the motor is decreased. In this situation, the operation of the brushless motor becomes more efficient and smoother. In addition, since the resonance is reduced, the noise generated by the motor is reduced.
The intervals d between the N-pole magnets 12 and the S-pole magnets 13, however, may incur some drawbacks. For example, due to the intervals d, the magnetic induction between the Hall element on the circuit board and the magnets 12, 13 is possibly interrupted. The poor magnetic induction results in erroneous judgment and deteriorates the overall performance of the motor.
For avoiding the poor magnetic induction caused by the chamfered edges of the magnets, the conventional motor is additionally equipped with an auxiliary-induction magnetic ring. The additional auxiliary-induction magnetic ring, however, increases the fabricating cost. Moreover, due to the size tolerance between the shaft and the auxiliary-induction magnetic ring or imprecise arrangement, a misalignment problem occurs. Moreover, if the auxiliary-induction magnetic ring is installed, the magnetization procedure should be performed again. In other words, the addition auxiliary-induction magnetic ring increases the fabricating cost and increases the process complexity.
Therefore, there is a need of providing a fan and a motor thereof to obviate the drawbacks encountered from the prior art.